1. Field of the Invention.
The present invention relates in general to a voltage reference source arrangement based on a bandgap voltage reference source.
2. Description of the Related Art
Bandgap voltage reference sources are commonly known. Conventionally, a bandgap voltage reference source arrangement includes a basic reference source having a negative temperature coefficient-and a compensation reference source having a positive temperature coefficient. The voltage provided by the compensation reference source is amplified such that the positive temperature coefficient substantially compensates the negative temperature coefficient of the basic reference source, and a reference voltage is obtained with a zero temperature coefficient.
A problem with such conventional reference source arrangement is that the compensation reference source may suffer from an offset voltage due to mismatches. Any such offset voltage will be amplified in the conventional reference source arrangement, with the consequence that the accuracy is poor.
In the art, there is a need for precision voltage sources. For instance, in battery operated devices, it is important that a user is signalled when the battery voltage drops below a threshold value, indicating that the battery should be replaced or recharged. Further, almost all kinds of analog-to-digital conversion and/or digital-to-analog conversion require a precision voltage reference sources for operating correctly.
Further, in the art, there is a further need for a voltage reference source with very specific characteristics. Specifically, in a practical example, there is a need for a voltage reference source having an output voltage of exactly 1V at a temperature of 27xc2x0 C. while delivering a current of 5 mA, whereas the temperature coefficient should be exactly xe2x88x921 mV/xc2x0 C. in a large temperature range.
It is a general objective of the present invention to provide a bandgap reference source arrangement with improved accuracy. Further, it is an objective of the present invention to provide a bandgap reference source arrangement where improved accuracy is an inherent property of the circuit design, without the need of complicated operations such as laser trimming, as is necessary in the current state of the art.
A further objective of the present invention is to provide a bandgap reference source arrangement with a predetermined non-zero temperature coefficient.
The invention is based on the insight that the mismatch and consequent offset in a compensation reference source is substantially random, and that the offsets of different compensation reference sources are uncorrelated. Based on this insight, the present invention provides a voltage reference source arrangement having a plurality of compensation reference sources. The number of such plurality corresponds to the amplification factor applied to the conventional compensation reference source. However, instead of amplifying the output of one single compensation reference source, the outputs of said plurality of compensation reference sources are added together. Each of said compensation reference sources may suffer from an offset, but in view of the fact that those offsets are uncorrelated, they may statistically eliminate each other. Formulated more correctly, the offset in the sum is less than the sum of the same offsets.
These and other aspects, characteristics and advantages of the present invention will be further clarified by the following description of a preferred embodiment of a voltage reference source arrangement in accordance with the invention.